1. Field of the Invention
This invention relates to gas springs, and particularly to a pneumatic spring capable of closing an electric circuit.
2. The Prior Art
It is known from the commonly owned U.S. Pat. No. 3,919,509 and from the German Utility Model No. 7304750 to install a gas spring between the body of an automotive vehicle and a cover pivoted to the body for angular movement about a horizontal axis to bias the cover away from a position in which it closes an opening in the body, and to connect a source of current on the vehicle body with a current-consuming device on the cover through the gas spring, thereby avoiding the need for a relatively fragile cable connection between the body and cover.
A gas spring commonly has a cylinder in whose cavity a piston is axially slidable and a piston rod fastened to the piston and axially projecting from the cylinder. A lubricant film on the internal cylinder wall prevents reliable electrical contact of the conventional piston with the cylinder wall. It has been proposed in the cited Utility Patent to transmit current through a gas spring by means of a contact on an outer face of the cylinder and another contact on the inner face of a sleeve mounted on the outer end of the piston rod and enveloping the cylinder. The sleeve protects the contact area against many particulate contaminants but has but little effect on atmospheric corrosion of the contacts.
It was proposed in the earlier U.S. patent conductively to connect the piston rod and cylinder by means of a helical compression spring fastened in the sealed cylinder cavity to the imperforate end wall of the cylinder and abuttingly engaging the piston when the latter approaches the end wall. While this arrangement safely avoids all problems of contact corrosion, the spring breaks a film of lubricant on the piston only if suitably shaped and carefully installed in the cylinder. Changes in shape or location of the spring after extended use may interfere with proper current flow. It would be difficult, if at all practical, to install the contact spring between the piston and the annular end wall of the cylinder, and the gas spring of the earlier patent has its greatest value when closing its contacts as it approaches its minimum length and the closed condition of the associated cover.